Light emitting diodes (LEDs) are increasingly used as a light source for lighting applications, such as, for example in conjunction with through-hole package assemblies. Various methods are used to produce white light from light emitting diodes.
One conventional method produces a white light using three different types of light emitting diodes (LEDs). This method generates the basic colors of red, green and blue to produce the white light. Unfortunately, when diffused light from R (red), G (green), and B (blue) LEDs is mixed to produce white light, several issues arise. These issues include variation of output color due to different utilized LEDs, complex drive circuits due to the different drive voltages needed by each different type LED, as well as different rates of deterioration under operating conditions.
Another method uses a blue light emitting device (LED) to illuminate a cerium-activated yttrium aluminum garnet (Y3Al5O12:Ce3+) phosphor material. In this method, the LED emits blue light that excites the phosphor. The phosphor is capable of absorbing at least a portion of the blue light and emitting a longer wavelength, i.e. broadband yellow light. The human eye perceives the combination of the blue light produced from the LED and the yellow light produced by the phosphor emission as white light. FIG. 1 shows an existing lighting device, such as a reflector cup 100, currently in use within the industry. In FIG. 1, reflector cup mounting package 100 includes a light source 110, shown here as a single LED located within reflector cup 120. Light source 110 provides uniform illumination throughout cavity 130 to surface 140.
In order to alter light output from reflector cup mounting package 100, it is a common industry practice to place a mixture 150 within cavity 130. The mixture 150 may include one or more phosphor compounds, such as the cerium activated yttrium aluminum garnet described above, with an optically-clear substance, for example optically-clear epoxy. The mixing results in the phosphor compound becoming suspended in the optically clear substance. When the suspended phosphor compound absorbs light from light source 110, the phosphor compound emits light based on an interaction of the absorbed light and the phosphor compounds.
Despite widespread industry use of the above-described device, this and other similar types of lighting devices have a number of disadvantages. One such disadvantage is a result of the process of mixing phosphor compounds with an optically-clear substance. It is difficult to achieve and duplicate a uniform mixture of the phosphor compound particles in the optically-clear substance. This difficulty results in a less than desirable uniformity of the light emission from the lighting device.
It would be desirable, therefore, to provide a method and device that would overcome this and other disadvantages.